The present invention relates to a method of producing workpiece having irregular cross section, and more particularly to a method of producing workpiece having irregular cross section by stamping a thin plate into a thick plate. In the method, predetermined scrap areas on the thin plate are continuously stamped so that some parts of these scrap areas are compressed and pushed toward non-continuous specific areas on the thin plate for forming thicker areas on the workpiece.
A conventional connecting terminal as shown in FIG. 1, or a contact element in a connector, or a contact element in a relay will frequently come into contact with other elements when the terminal, the connector or the relay is in use. It is a common practice to increase the thickness of the areas of such connecting terminal or contact element that are frequently contacted with other elements, so that the terminal or the connector or the relay may have longer useable life or higher wear resistance. Such element having areas of different thickness is usually referred to as the workpiece having irregular cross section.
In a conventional method for producing the above-described workpiece having irregular cross section, a plate having a uniform thickness T corresponding to a largest thickness to be formed on the workpiece is selected for use. Areas on the plate that are to be thinned for forming thinner areas on the workpiece are fabricated by milling, as shown in FIG. 2, to obtain a desired thickness t. Thereafter, the milled plate is further rolled or ground to provide a plate having the desired irregular cross section as that to be formed on the workpiece. The plate is then stamped to obtain the workpiece having a desired profile and the desired irregular cross section.
In the process of milling the plate to obtain the desired irregular cross section, high temperature tends to occur at the surface being milled and results in changes of the physical properties of the plate, such as uneven thickness or varied hardness. Such changes in physical properties frequently cause unexpected changes in the thickness of the milled plate and accordingly, difficulties in subsequent stable fabrication of the plate. Moreover, the plate selected for use has an initial thickness corresponding to that for the thickest area on the complete workpiece. A large part of the thick plate is milled to meet the thickness for the thinner areas to be formed on the complete workpiece and therefore unnecessarily produces a large amount of scraps. Burrs and warps also tend to occur at ends and edges of the milled surfaces to cause poor quality of the produced workpiece. In the event the workpiece has discontinuous thicker areas, such milling process must be locally proceeded at such thicker areas one by one and the tool used to mill the plate must be differently adjusted for each area to obtain the desired stepped surface of the workpiece. Such milling process is time consuming and increases the manufacturing cost thereof and it is impossible to proceed the milling at different stages in an automated manner.
It is therefore a primary object of the present invention to provide a method of producing a workpiece having irregular cross section by stamping a thin plate into a thick plate. In this method, a plate having a uniform thickness corresponding to a smallest thickness to be formed on the workpiece is used, so that cost and time that is otherwise needed to mill the plate can be saved and scrap that would be produced in the stamping is largely reduced to lower the manufacturing cost of the workpiece.
To achieve the above and other objects of the present invention, there is provided a method of producing a workpiece having irregular cross section, in which a thin plate having a uniform thickness corresponding to that of a thinner area to be formed on the workpiece is used. Multiple stamping heads having different and gradually increased bevel angles are used one by one to stamp one or two sides of the thin plate at predetermined scrap areas, so that parts of the scrap areas are gradually compressed and pushed toward specific areas that are to have a larger thickness on the workpiece. When the specific areas bump to a predetermined height through continuous stamping of the scrap areas, stamping molds are used to downward stamp the bumped areas into a predetermined shape. Thereafter, the remained scrap areas on the thin plate are removed to obtain the desired workpiece. With the method of the present invention, thickness of the workpiece at different areas can be precisely controlled and the producing of a workpiece having discontinuous thicker areas can be achieved through automated fabrication processes. The method also enables largely reduced scrap and manufacturing time and cost in forming the workpiece having irregular cross section.